The Characidae
family is an extremely large one that includes the various tetra species
commonly found in the pet trade. The genera Pygocentrus contains what
are though of as true piranhas or caribes. This genera includes P. nattereri,
the red-bellied piranha, which grows to about 12 inches. The genera Rooseveltia has
become invalid, because it had been previously used on another animal species.
The genus Serrasalmus is a large complex of as many as 12-14 closely
related species. This classification has been revised several times. The
most common “piranha” in the class is S. rhombeus, which
grows up to 18 inches. The species undergo so many morphological changes
as they mature that the rhombeus is called “white piranha” and “black
piranha.” Generally speaking these fish have laterally compressed bodies,
and short powerful jaws with triangular interlocking teeth. They are carnivorous
and will bite anything that moves.